Kyung-Sook Hyun

High-speed and highly reliable InP/InGaAs avalanche photodiode for optical communications

We present a review of the characteristics of several different types of high speed InGaAs/InP avalanche photodiode (APD)s that we have developed for different guard ring depth and for different main p-n junction shape. The APD structure that we propose consists of a greatly reduced width in InP multiplication layer and a high doping concentrated electric field buffer layer, where we also adopted a floating guard ring and a shaped main junction with recess etching for a reliable operation of an APD. We obtained high reliability APDs, which are tested for two-dimensional gain behavior and for accelerated life tests by monitoring dark current and breakdown voltage. The gain and bandwidth product of the best of our APDs was measured as high as 80 GHz.

Resonant characteristics of multimode interferometer coupled square ring semiconductor resonators

This work reports the spectral characteristics of coupled square ring semiconductor resonators. For a single mode operation, the square ring cavities coupled with multimode interferometers (MMIs) are proposed and fabricated using the epitaxial layers of 1.55 microm center wavelength InGaAsP-InP multiple quantum wells. Resonant characteristics can be tailored by varying the parameters of the cavity size or the waveguide width. By using the MMI coupled square ring cavity, a stable single spectral lasing mode was obtained in various combinations of square cavities.

Pre-breakdown suppression in planar InP∕InGaAs avalanche photodiode using deep floating guard ring

We propose a deep floating guard ring (DFGR) structure which effectively prevents the curvature breakdown of a central junction in a planar InGaAs∕InP avalanche photodiode (APD). In order to investigate the DFGR APD performance, the dark current, photocurrent, and radial dependence of gain were measured and analyzed. In addition, the relation between breakdown voltage and multiplication layer thickness was calculated using a nonlocal history-dependent model. Reliable operation in the device center region was examined by measuring the radial gain. As a result, it has been confirmed that the DFGR is very useful for an APD with a very thin multiplication layer.

Selection of lasing direction in single mode semiconductor square ring cavities

We propose and demonstrate a selection scheme of lasing direction by imposing a loss imbalance structure into the single mode square ring cavity. The control of the traveling direction is realized by introducing a taper-step section in one of the straight waveguides of the square ring cavity. It was shown by semi-analytic calculation that the taper-step section in the cavity provides effective loss imbalance between two travelling directions as the round trip repeats. Various kinds of square cavities were fabricated using InGaAsP/InGaAs multiple quantum well semiconductor materials in order to test the direction selectivity while maintaining the single mode. We also measured the pump power dependent lasing spectra to investigate the maintenance property of the lasing direction. The experimental results demonstrated that the proposed scheme is an efficient means for a unidirectional lasing in a single mode laser.

Lasing of Coupled Guided Modes in Modified Hollow Hexagonal Semiconductor Cavities

Coupled guided modes, proposed in various modified hollow hexagonal cavities each attached internally to a hexagon, were demonstrated by investigating the laser oscillations in semiconductor cavities. The mode spacing between two adjacent lasing peaks decreased as the size of the internal hexagon increased, due to the increased round-trip length of the coupled guided modes. The linear dependency of the inverse mode spacing to the calculated round-trip length strongly confirmed the lasing of the coupled guided modes. The proposed modes in common-sized external cavities showed resonance structure that could be adjusted widely by controlling the size of the internal hexagon.

Single Mode Lasing in InGaAsP/InP Semiconductor Coupled Square Ring Cavities

This work reports the stability of the resonant characteristics in multimode interferometer coupled square ring semiconductor cavities. Based on the analysis of single square ring cavities, the single mode operations in the multimode interferometer coupled ring cavities are analyzed and the devices are demonstrated on the semiconductor multiple quantum well epitaxial structure. By varying the lasing conditions such as substrate temperature and input pump power, single resonant mode operations are also observed.

Bow-tie Mode Lasing in a Grooved Rectangular Semiconductor Microcavity

Bow-tie modes were proposed in a grooved rectangular resonator and their lasing characteristics were investigated in semiconductor microcavities. The observed spacing between two adjacent lasing peaks from the grooved cavity was reduced compared to that of 4-bounce whispering gallery modes (WGMs) from the same-sized simple rectangular cavity due to increased round-trip path length of the bow-tie modes. The lasing spectra of bow-tie modes obtained from two adjacent corners showed highly correlated patterns while those of 4-bounce WGMs did not.

Four channel Mach–Zehnder demultiplexer using multimode interferometers in InP/InGaAsP

Abstract1 × 4 and 4 × 4 wavelength demultiplexers using multimode interferometer (MMI) were successfully demonstrated in InP/InGaAsP. Optical transmission characteristics were measured for each input to output for transverse electric (TE)/transverse magnetic (TM) modes. Reduced polarization sensitivity less than 0.3 nm was achieved in 1 × 4 MMI-MZ demultiplexer with −15 dB channel-to-channel cross talk. For 4 × 4 MMI-MZ demultiplexer, the optical crosstalk was well below −16 dB in TM mode for all input to output measurements.

Lasing characteristics of resonance modes in a racetrack cavity with hexagonal corners

We propose resonance mode in a racetrack cavity with hexagonal corners, in which the modes are guided by both boundaries of the corner. The modes were demonstrated by investigating the laser oscillations in semiconductor cavities.

Selection of the lasing direction using S-bend in the semiconductor cavities

The selection of lasing direction in micro cavity is demonstrated by using s-bend in the rectangular cavity. The parameter of S-bend section is calculated to minimize the propagation loss and optimized to serve good selectivity.